With lots of rural and blue-collar voters, Wisconsin may be Santorum's last best shot to hurt Romney

With victories now in three key Great Lakes primaries – Illinois, Ohio and Michigan – Mitt Romney can make it four straight in Wisconsin April 3 and deal another big blow to Rick Santorum’s presidential prospects.

But Romney could find Wisconsin a tougher challenge than he faced in Illinois Tuesday, thanks to differences in the political makeup of these two neighboring states.

Romney was boosted in Illinois by big margins among upper-income, college-educated and suburban voters -- groups he has won across the industrial Midwest.

But those voters have a smaller political footprint in Wisconsin than they do in Illinois.

By the same token, Wisconsin boasts lots of blue-collar and rural voters, two groups that have been more supportive of Santorum.

These differences don’t by any means assure a Santorum victory in Wisconsin. But they do give him some hope of ending Romney’s Midwestern winning streak and slowing his march to the nomination. In fact, Wisconsin may be Santorum's last chance for a while to truly knock Romney off stride.

Wisconsin is closer in its political profile to Michigan and Ohio – where Romney’s victories were very narrow -- than to Illinois, which Romney won by double digits.

The chart below shows some notable differences between the electorate in the Illinois GOP primary Tuesday and in Wisconsin's GOP presidential primary in 2008:

Rural voters made up only 11% of the Illinois vote Tuesday. They made up 41% of the vote in Wisconsin’s GOP presidential primary four years ago. The Illinois electorate Tuesday was split almost 50/50 between college grads and voters with no college degree. In Wisconsin’s 2008 primary, non-college voters outnumbered college grads by 20 percentage points.

These comparisons aren’t perfect, since 2008 and 2012 were very different races. But the numbers reflect real political distinctions between the two states. Rural voters (a group Santorum easily carried Tuesday) have less impact on statewide GOP races in Illinois than they do in Wisconsin. And voters in the sprawling Chicago suburbs (a group Romney easily carried Tuesday) play a more numerically dominant role in Illinois than voters in the Milwaukee suburbs do in Wisconsin.

Even the nature of the suburban vote differs in the two states. The suburban counties outside Chicago are somewhat more upscale, less Republican and less conservative than the suburban counties outside Milwaukee. In the biggest suburban county in Illinois, DuPage, the Republican share of the presidential vote was 54% in 2004 and 44% in 2008. In the biggest suburban county in Wisconsin, Waukesha, the GOP presidential vote was 67% in 2004 and 63% in 2008.

These differences matter when you consider the fault lines the Romney-Santorum fight has followed elsewhere, including in the three big Midwest primaries so far.

Romney has carried college grads:

And suburbanites:

While Santorum has easily won rural voters:

And beaten or matched Romney among non-college voters:

Other factors will also be in play in Wisconsin. It has helped Rommey’s fortunes in the Midwest that evangelical voters aren’t the dominant political force they are in Southern states. Wisconsin’s open primary means a sizeable non-Republican vote, a category that has leaned toward Romney in some states and Santorum in others. The only big ad campaign on the air right now is coming from a pro-Romney PAC, and Romney’s money advantage could hobble Santorum. But Wisconsin’s smaller TV markets aren’t as prohibitively expensive for the underfunded Santorum campaign as Chicago’s costly media market was.

All things being equal, Wisconsin may be the closest thing in the GOP race to a level playing field next month. It offers Santorum the chance to win a major Midwest battleground with an overlapping coalition of rural voters, social conservatives and blue-collar voters.

The Wisconsin Voter is a blog about elections, political trends and public opinion in Wisconsin and the Upper Midwest. It is less about politicians than the people who elect them. It’s aimed at political junkies and general readers alike. Its subjects include:

The role this state and region play as electoral battlegrounds.

Voting patterns and trends at the local, state and regional level.

What makes voters here different from voters in other places.

Public opinion and the election climate.

Craig Gilbert is the Journal Sentinel's Washington, D.C. Bureau Chief and national political reporter.

Charting how each of Wisconsin’s 72 counties has trended politically compared to the U.S. as a whole over 60 years of presidential voting. Use the pull down menu to see charts for individual counties. Click here for an explanation of how the charts were done and how to read them.